Fully conjugated heterocyclic aromatic rod-like polymer poly-p-phenylene- benzobisoxazole (PBO) and coil-like poly-(3-hexylthiophene) (P3HT) were applied as opto-electronically active layer. The two polymers mixed with nano-carbon particles, having excellent optical absorption and electric conductivity, of [6,6]-phenyl C61-butyric acid methyl ester (PCBM) or esterified multi-wall carbon nano-tube (MWNT-COOC10H21) as well as a hole transporting layer of PEDOT:PSS. Photovoltaic (PV) cells of indium-tin-oxide (ITO)/PEDOT:PSS/nano-carbon particle:fully conjugated polymer/Al were fabricated for optical and electrical characterizations. Tri-layered structure of ITO/PEDOT:PSS/PBO/PCBM/Al produced a straight current-voltage relation showing no PV effects. Upon changing the active layer into PCBM doped P3HT layer (PCBM:P3HT), it produced good PV effects suggesting that the doped layer had a penetrating network to facilitate the PV effects. When PCBM or MWNT-COOC10H21 was doped into P3HT, the device PV effects were increased significantly with nano-carbon particle concentration. The direct-current electric conductivity parallel to the film surface (£m¡ü)was increased with the nano-carbon particle concentration. By changing the thickness of hole transporting PEDOT:PSS and of opto-electronically active layers, it was found that when the PEDOT:PSS layer was decreased from 90 nm to 32 nm, there was a slight increase of PV cell efficiency. The active layer of PCBM:P3HT with a thickness of 99 nm had the best optical absorption and charge transport leading to an increase of PV cell efficiency.

Opto-electronics of non-fully conjugated molecules was demonstrated successfully in this research as light emitting diodes (LEDs). A series of benzoxazole poly[2,2-(m-2-hydroxyl phenylene)-4-4¡¦-hexafluoroisopro- pane-bibenzoxazoles] (6F-PBO-OH, Am) and benzimidazole poly[2,2¡¦- (2-hydroxy-o-phenylene)-5,5¡¦-bibenzimiazole] (OH-Pbi, B(1-m)) were copolymerized for coil-like non-fully conjugated poly-(Am-co-B(1-m)) for luminescence investigation. UV-Vis absorption of the non-fully conjugated copolymers showed superposition of individual absorption response from the two chemical components of the copolymer. However, the photoluminescence (PL) and the electroluminescence (EL) emissions had a red shift with increasing OH-Pbi content. It seemed to suggest that OH-Pbi was more charge delocalized than 6F-PBO-OH. In mono-layer LEDs, the diode threshold voltages were about at 2 ~ 3 V and the EL showed a green emission. Tunable emission was not observed in varying the m value of the copolymers. Composites of copolymer, poly(Am-co-B(1-m)) and multi-wall carbon nanotube (MWNT) were in-situ synthesized for mono-layer LED fabrication. Few MWNT aggregation was observed via the field-emission scanning electron microscopy. It was a success in dispersing MWNT in the copolymers. There was a red shift with MWNT addition in the PL and the EL emissions. The diode threshold voltages were about at 2 ~ 5 V and the EL emission still showed a green emission. According to this study, MWNT was inconsequential on the PL and the EL emissions of the copolymers up to 2 wt. %.

Polymer photovoltaic cell (PV cell) utilizes a polymer to absorb photons for generating excitons. When excitons are separated into electrons and holes, the device has the photovoltaic effect. Polymer light emitting diode (PLED) injects electrons and holes respectively from cathode and anode into a polymer emission layer. Some of the electrons and the holes would recombine to induce light emission. This research used a heterocyclic aromatic rigid-rod polymer poly-p-phenylene- benzobisoxazole (PBO) as the opto-electronic layer, and a conducting material of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonic acid) (PEDOT:PSS) as the hole transport layer. PV cells were fabricated using indium-tin-oxide (ITO) as anode and aluminium as cathode. Same layer arrangement was applied for PLEDs. These two kinds of devices were measured for electrical and optical response. It was evidenced that the addition of PEDOT:PSS layer facilitated the separation of excitons into electrons and holes at the PBO/PEDOT:PSS interface. Insertion of a LiF layer between PBO layer and Al cathode reduced their energy band gap and facilitated charge transport leading to an enhanced efficiency for PV cells and PLEDs. Thickness variations were found on spun PBO layer. According to emission intensity, we knew that the PBO layer quality was significant for electroluminescence. Introduction of a PEDOT:PSS layer improved the interface between ITO and PBO. The thickness of PEDOT:PSS layer depended on the ITO surface roughness. With a PEDOT:PSS layer, the opto-electronic efficiency of PV cell and PLED was improved.

Luminescent emission of non-fully conjugated homopolymers was successfully demonstrated as light emitting diodes (LEDs) in this research. Coil-like heterocyclic aromatic poly[2,2-(2,5-dialkyloxyphenylene)-4-4¡¦-hexafluoroisopropanebibenzoxazo- les] (6F-PBO-CnOTpA, with n = 10, 15, and 20) was synthesized, and polymer composites of 6F-PBO-CnOTpA was in-situ synthesized with acidified multi-wall carbon nanotube (MWNT- COOH). The non-fully conjugated coil-like heterocyclic aromatic homopolymer was synthesized by reacting 2,2,bis-(3-amino-4-hydroxy[henyl]-hexafluoropropane with 2,5-dialkyloxyterephthalic acid (CnOTpA) for 6F-PBO-CnOTpA, with n = 10, 15, and 20. In addition, MWNT was acidified for connecting the carboxylic group (-COOH) to reduce its aspect ratio and entropy induced aggregation. MWNT-COOH was analyzed using elemental analysis (EA) and viscometry to validate the effects of acidification period. The EA result seemed to suggest that the oxygen content increased, and the carbon and the hydrogen contents decreased with acidification period. The inherent viscosity (£binh) decreased according to acidification period suggesting that the aspect ratio was indeed decreased. A hole transport layer of PEDOT¡GPSS was applied for multi-layer LEDs,. The LEDs all showed a threshold voltage about 4 V also for the composites of 6F-PBO-CnOTpA in-situ polymerized with MWNT-COOH. The 6F-PBO-CnOTpA LEDs with and without MWNT-COOH showed an electroluminescence emission range of 400 to 750 nm.

ABSTRACT Light emitting diodes of non-fully conjugated coil-like homopolymers and fully conjugated rigid-rod homopolymers with electron withdrawing or donating group were studied. A series of Poly[2,2-(m-2-X-phenylene)-4-4¡A-hexafluoroisopropane- bibenzoxazoles] (6F-PBO-X, with X = amine, hydrogen and nitro) and poly-p-(2-X- phenylene)-benzobisoxazole (PBO-X, with X = amine, hydrogen and nitro) were synthesized for light emitting diode applications to observe electroluminescence emission affected by electron withdrawing or donating group. All polymers were fabricated identically to form bi-layer light emitting diodes. In the devices, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonite)(PEDOT:PSS) was applied to be a hole transport layer; indium tin oxide (ITO) was the anode; and aluminum was the cathode. Devices of the non-fully conjugated coli-like polymers (6F-PBO-X) and the fully conjugated rigid-rod polymers (PBO-X) all showed threshold voltage about 4 V. In the electroluminescence (EL) spectrum, the maximum intensity of non-fully conjugated polymer (6F-PBO-X) with amine (-NH2), hydrogen (-H) or nitro (-NO2) functional group was at 499 nm, 505 nm and 515 nm, respectively, showing a 20 nm wavelength shift. From ¡VNH2, -H and ¡VNO2 groups, their Commission International de l`Eclairage (C. I. E.) coordinates were (0.30, 0.46), (0.34, 0.45) and (0.40, 0.46), respectively. The EL maximum intensity for fully conjugated rigid-rod polymer PBO-X was at 521 nm (-NH2) and 474 nm (-NO2) showing a 50 nm wavelength shift. Their C. I. E. coordinates were (0.42, 0.45) and (0.25, 0.38), respectively. This is attributed to the fully conjugated, collinear, coplanar, rigid-rod polymers (PBO-X) backbone readily affected by the push-pull functional groups showing a large red shift.